The present invention relates to an arrangement for cleaning the bottom of an electrolytic tank of solids settled thereon, said arrangement comprising elements to be moved along the bottom or at least in the vicinity thereof in order to detach solids from the bottom.
In electrolytic processes, metals such as copper, nickel and zinc, are precipitated on the surfaces of cathodes located in the electrolytic tank, starting either with metal anodes that are dissolved into the electrolyte present in the electrolytic tank, or with metal ions that are already dissolved into the electrolyte. However, all solids are not precipitated onto the cathode surfaces, for example precious metals and solid impurities present in the electrolyte. Therefore on the bottom of electrolytic tanks, there are accumulated, along with the metal refining process, various solids that must from time to time be removed from the tank, for instance because said solids contain valuable ingredients, such as precious metals, or because a thicker solids accretion threatens the purity of the cathode obtained from the electrolytic process.
Usually the solids accumulated in the electrolytic tank is are at least partly very finely divided and only somewhat heavier than the electrolyte, wherefore it is difficult to separate the solids from the electrolyte. During the electrolytic process, the circulation of the solids from off the bottom of the electrolytic tank is very harmful, because in that case there is a particularly high risk that the solids proceed onto the cathode, and this would essentially weaken the purity of the metal to be produced.
The removal of the solids accumulated on the bottom of an electrolytic tank usually requires that the whole electrolytic process must be interrupted, which reduces the efficiency per time, i.e. the productivity of the electrolytic plant. Hence the removal of solids must be arranged so that it forms part of the process of replacing the electrodes, i.e. anodes and cathodes; this, however makes the replacement process complicated and slow, and also restricts the removal of solids to take place in the rhythm dictated by the process of replacement. Moreover, a remarkable amount of the electrolyte must be first removed from the tank and then fed back therein, which generally leads to harmful effects in the electrolyte quality and causes a lot of extra work. Into the solids treatment system, there also flows a remarkable amount of electrolyte, which must be replaced with new and may be harmful in the further treatment of the solids. Moreover, the manual washing of the electrolytic tanks makes the process clearly more labor-intensive and subjects the employees to various health hazards, among others owing to the effects of the ingredients contained in the splashes and spray emanating from the tank. In addition, owing to the personnel required by the washing of the tanks, the automatization of the electrode treatment is often nearly impossible, which further increases the labor demand in an electrolytic plant.
From U.S. Pat. No. 6,299,756, there is known a separating element for separating the bottom part of an electrolytic tank from the rest of the tank space in connection with the removal of the solids settled on the tank bottom. In said publication, in the electrolytic tank there are arranged support and control members that form the trajectory of the separating element, so that the separating element can be placed in the electrolytic tank and removed therefrom through a space provided in between at least one end wall and the electrode placed nearest to said end wall. In the separating element, there can be attached means for feeding cleaning agent into the bottom part of the electrolytic tank, or mechanical devices for detaching solids. The detached solids are removed from the tank through an outlet aperture provided in the tank bottom, or by means of a separate pump.
The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve an improved arrangement for cleaning the bottom of an electrolytic tank of solids settled thereon, said arrangement comprising means to be moved along the bottom or at least in the vicinity thereof for detaching solids off the bottom. The essential novel features of the invention are apparent from the appended claims.
According to the invention, the arrangement also comprises at least one movable suction element whereby at least part of the solids accumulated on the bottom are conducted out of the tank. By means of the movable suction element, there is achieved an extremely efficient removal of solids from the tank.
The suction element according to the invention is a suction nozzle arranged essentially transversally to the motional direction of the arrangement, said suction nozzle preferably extending essentially along the whole width of the tank and being provided with at least one feed aperture and at least one discharge aperture. When the suction nozzle is placed transversally and extends to the whole width of the tank, there is achieved an extremely intensive suction effect, and the solids are removed by one motion of said suction element, by moving it from one end of the tank to the other end.
The suction element according to the invention comprises a housing, at the bottom part whereof there is formed at least one feed aperture, and in which housing there is preferably formed at least one discharge aperture that can be connected to a suction conduit. According to a preferred embodiment, in the suction nozzle there are made several feed apertures, in which case the apertures can serve as sieve members, thus breaking the solids accretions into smaller parts. According to another embodiment, in the suction nozzle there is made a longitudinal, slot-like feed aperture that extends to the whole width of the suction nozzle. Now the solids can be removed extremely efficiently, and at the same time the blocking of the feed apertures of the suction element can be avoided. According to a preferred embodiment of the invention, in connection with the suction nozzle, there is arranged at least one nozzle for feeding cleaning agent. By means of the nozzle for feeding cleaning agent, the proceeding of the solids into the suction nozzle can be boosted.
A suction nozzle in a preferred embodiment of the arrangement according to the invention comprises means for pressing the suction nozzle towards the tank bottom. Now an optimal solids removal effect of the suction nozzle can be ensured. The suction nozzle can be provided with mechanical solids detaching means, in which case the cleaning effect created by the suction nozzle is further improved. When the suction element according to the invention is attached to a separating wall element which at the same time serves as a drive element, there is obtained an extremely effective arrangement for removing solids from the bottom of an electrolytic tank.